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Forces look easy until a question asks why a sharp knife cuts better than a blunt one, or why a balloon rubbed on wool sticks to a wall. This post sorts the forces you meet in Class 8 into contact and non-contact types, explains pressure with worked numbers, and ends with a practice plan.
Where are force and pressure in the current book?
NCERT's Class 8 science book is now Curiosity, marked "Reprint 2026-27". Forces are in Chapter 5, "Exploring Forces". Pressure is in Chapter 6, "Pressure, Winds, Storms, and Cyclones". The older Class VIII book had one chapter called "Force and Pressure". The definitions match, and Curiosity also covers weight, the spring balance, winds and cyclones.
What are contact and non-contact forces?
Chapter 5 defines a force as a push or a pull, measured in newtons (N). It sorts forces by whether the objects must touch.
Contact forces act only when objects touch, directly or through a stick or rope:
Muscular force: from our muscles when we walk, lift or push. Muscles also move food along the gut and pump blood.
Friction: acts between two surfaces in contact and opposes motion. Our separate post on friction in Class 8 covers it in detail.
Non-contact forces act across a gap:
Magnetic force: like poles repel and unlike poles attract. In the book's ring-magnet activity, one magnet floats above another.
Electrostatic force: a plastic scale rubbed with polythene pulls small pieces of paper. Two balloons rubbed with wool push each other away, while a balloon and the wool attract. Like charges repel and unlike charges attract.
Gravitational force: the Earth's pull on every object. The book points out it is always attractive, while magnetic and electrostatic forces can attract or repel.
Weight is the gravitational force on an object, so it is also measured in newtons. A spring balance measures it.
What is pressure, and why does area matter?
Chapter 6 defines pressure as force per unit area. Its SI unit is the newton per square metre (N/m²), also called the pascal (Pa).
Pressure = Force ÷ Area
The book's examples: a bag with broad straps is easier on the shoulders, and people carrying loads on their heads put a round cloth underneath. In both cases a larger area means less pressure for the same weight. A sharp knife works the other way: the small area of the edge means large pressure.
The chapter also shows that liquids exert pressure on the walls of their container, in all directions, and that the pressure at the bottom depends on the height of the liquid column. Air exerts pressure too.
Worked example: same student, three positions
A student weighs 480 N. Each foot covers 0.02 m² of floor.
Standing on both feet: area = 2 × 0.02 = 0.04 m². Pressure = 480 ÷ 0.04 = 12,000 Pa.
Standing on one foot: area = 0.02 m². Pressure = 480 ÷ 0.02 = 24,000 Pa. Half the area, twice the pressure.
Lying flat: suppose the body touches 0.4 m². Pressure = 480 ÷ 0.4 = 1,200 Pa.
The force is the same in all three cases; only the area changes. This is why spreading your weight over a wide plank makes it easier to cross soft mud.
Check with the book's own figure. Chapter 6 says the air above an area of 15 cm × 15 cm pushes with a force of about 2,250 N. Convert the area first: 15 cm × 15 cm = 225 cm², and 1 m² = 10,000 cm², so the area is 0.0225 m². Pressure = 2,250 ÷ 0.0225 = 100,000 Pa. We are not crushed because, as the book explains, the pressure inside our bodies balances it.
Which mistakes cost marks?
Leaving area in cm². Convert to m² before dividing, or your answer in pascals will be 10,000 times too small.
Confusing force and pressure. A heavier object does not always press harder; area matters.
Mixing mass and weight. Mass is in kilograms, weight in newtons. Curiosity's exercises point out that weight on the Moon is one-sixth of weight on Earth, but the amount of matter, the mass, does not change.
Calling gravity "sometimes repulsive". It only attracts.
Calling friction non-contact. It needs surfaces to touch.
A practice routine for this chapter
Day 1: From memory, list five forces and label each contact or non-contact, with one example.
Day 2: Solve three pressure questions of your own: a brick lying on each of its three faces.
Day 4: Explain, in two sentences each, why school bags have broad straps and why nails have pointed tips.
Day 7: Redo the worked example with a 600 N weight without looking (answers: 15,000 Pa, 30,000 Pa, 1,500 Pa).
If you find it hard to picture how pressure changes with area or depth, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read. When you reach Class 9, our guide to force and the laws of motion builds on this chapter.
Pick three objects at home tonight and write whether each is held, pushed or pulled by a contact or a non-contact force.
